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Solar Energy IV

Solar Energy IV. Hydroelectricity and OTEC. Hydro power has a very long history with watermills appearing as early as 100 BC. By 1200 it was used to operate hammers in ironworks. By 1500 it was the primary source of industrial power.

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Solar Energy IV

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  1. Solar Energy IV Hydroelectricity and OTEC

  2. Hydro power has a very long history with watermills appearing as early as 100 BC. • By 1200 it was used to operate hammers in ironworks

  3. By 1500 it was the primary source of industrial power. • Rivers and streams were a critical source of power and transportation in the settling of America.

  4. First Hydroelectric Generator • Located at Cragside, a country house in Northumberland, England. • In 1870, water from one of the estate's lakes was used to drive a Siemensdynamo in what was probably the world's first hydroelectric power station.

  5. Today Hydropower is used mainly for generating electricity

  6. Water cycle as a great big heat engine

  7. Generators inside Hoover Dam

  8. Convert Potential Energy of Water Into Kinetic Energy to Run a Generator • mgh=mv2/2 • h is called the “head” of the dam • Modern hydroelectric plants convert ~90% of PE into electricity

  9. High Head Dams • h is up to 1000ft. • A lot of energy per liter of water that flows through. • Can get by with smaller flows.

  10. Low Head Dams • As low as 10 ft. • Not much energy per liter of water. • Need a higher flow rate to get as much electricity

  11. Sample Calculation • Useful information: 1 liter of H2O has a mass of 1kg. • Height of Hoover Dam = 221 m • Power rating of Hoover Dam is 2,451 MW. • Find the amount of water that flows through the dam per second if it is 90% efficient.

  12. Electrical power form 1 liter of water per second. • P =(0.9)(1kg/s)(9.8 m/s2)(221m) =1.949kW

  13. US Hydroelectric Production

  14. Existing hydroelectric plants (yellow) and potential high head/low power energy sites (orange)

  15. Principal Dams in the US

  16. Top Ten Countries for Hydroelectricity

  17. Top Ten Largest Hydroelectric Plants

  18. Three Gorges Dam(World’s Largest)

  19. Ten largest Dams Under Construction

  20. Whacky Idea (2007)Red Sea Dam The idea is to dam the Red Sea at its southern end where the Bab-al-Mandab Strait is only 18 miles (29 km) wide. Natural evaporation would rapidly lower the level of the enclosed Red Sea. Water allowed back into the sea would drive turbines to generate electricity. It is claimed that up to 50 gigawattswould be generated, dwarfing all other power schemes.

  21. Advantages to hydroelectric power: • Fuel is not burned so there is minimal pollution. • Water to run the power plant is provided free by nature. • Hydropower plays a major role in reducing greenhouse gas emissions. • Relatively low operations and maintenance costs. • The technology is reliable and proven over time • It's renewable - rainfall renews the water in the reservoir, so the fuel is almost always there.

  22. Reservoirs can be used for other purposes such as irrigation, recreation, flood control

  23. Disadvantages • Lifetime of 50 to 200 years because of silting. • Large environmental changes downstream. • Loss of free flowing water. • Loss of land flooded by reservoir. • Often upstream from large population centers (Huge catastrophe if dam fails.)

  24. High investment costs Hydrology dependent (precipitation) Inundation of land and wildlife habitat Loss or modification of fish habitat Fish entrainment or passage restriction Changes in reservoir and stream water quality Displacement of local populations

  25. Dam Failures • From 1918-58 there were 33 dam failures in the US resulting in 1680 deaths. • Between 1959 and 65 there were 9 large failures worldwide. • It is unusual, but a significant hazard. • Terrorists?

  26. Water pouring out of the reservoir of the Teton Dam in Idaho following its catastrophic failure on June 5, 1976. Teton Dam Failure

  27. Ocean Thermo Electric Conversion • Use temperature difference between the surface and deep water to drive a heat engine. • Typically very low efficiency, but no cost for fuel. • Typically T 20K and Th20K, thus ec=T/Th 20/300=6.7% Real efficiency more like 2-3%

  28. Requires a huge flow of water. • A 100 MW plant would require approximately 25,000,000 liters per second of both warm and cold water.

  29. Use in locations with warm surface waters. T>17C • Predictable power output since T is very stable over the course of a day.

  30. Not a whole lot currently being developed. • 1930’s : concept plant built near Cuba generated 22kW of power, but used more than it generated. • 1970’s : small test plant built in Hawaii. • No government support since the 1980’s.

  31. Other Ideas • Large underwater turbines anchored to the sea floor. • Ex: Gulf stream has a steady flow that is 1000 time larger than the Mississippi River with a maximum velocity of 4mph.

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